1. Field of the Invention
The present invention relates to the manufacture of integrated circuit devices and, in particular, to utilization of atomic oxygen to provide a better stoichiometric silicon dioxide structure with fewer dangling bonds than results from oxidation processes currently used in integrated circuit fabrication. Addition of atomic nitrogen to the oxidation process results in an improved nitrogen-doped thermal oxide.
2. Description of the Related Art
FIG. 1 shows a conventional MOS transistor structure that includes spaced-apart source/drain (S/D) regions 10 of one conductivity type (e.g., n-type) formed in semiconductor material 12, typically silicon, having a conductivity type (e.g., p-type) opposite that of the source/drain regions 10. The spaced-apart source/drain regions 10 define a channel region 14 therebetween. A conductive gate region 16, typically polysilicon, overlies the channel region 14 and is separated therefrom by a gate dielectric layer 18, illustrated in FIG. 1 as silicon dioxide about 40-50 xc3x85 thick.
FIG. 1 shows the normal molecular structure of the gate silicon dioxide 18 as consisting of four oxygen atoms bonded to a silicon atom, each oxygen atom being shared by four adjacent silicon atoms. However, as further shown in FIG. 1, due to the imperfect nature of current semiconductor integrated circuit fabrication techniques, silicon dioxide formed in accordance with these conventional techniques contains xe2x80x9cdanglingxe2x80x9d silicon bonds, represented by the xe2x80x9cxxe2x80x9d in the silicon dioxide structure shown in FIG. 1. That is, sites exist within the silicon dioxide structure 18 where an oxygen atom should be present, bound to four adjacent silicon atoms, but is not. These stoichiometric imperfections in the silicon dioxide material 18 can cause performance deficiencies in the resulting integrated circuit device.
It would, therefore, be highly desirable to have available a technique for forming a better stoichiometric silicon dioxide structure with less dangling bonds than results from currently available techniques for forming silicon dioxide.
The present invention provides a method that utilizes atomic oxygen in a fast ramp furnace to generate a more thorough silicon oxidation process. By placing a large surface area of a metal-oxide, ceramic material, e.g., aluminum oxide (Al2O3), into the fast ramp furnace and heating it with the silicon wafers in Argon during the ramp cycle, the reactor can be brought to temperature without any oxidation occurring. Oxygen is then passed through the heated ceramic to generate atomic oxygen, which, as is well known, is more highly reactive than molecular oxygen. This more reactive oxygen provides a better stoichiometric gate oxide with less dangling bonds than standard oxidation processes. As a variant of this process, atomic chlorine can be generated in a similar manner as a silicon pre-clean step prior to introduction of the oxygen gas into the reactor. As a further variant, molecular oxygen and molecular nitrogen can both be dissociated to atomic form to provide nitrogen-doped thermal oxide.
In an alternative embodiment of the invention, the atomic oxygen is generated at a remote source, e.g., as an oxygen plasma, and then introduced to the furnace chamber containing the silicon to be thermally oxidized. UV radiation can also be utilized to generate the atomic oxygen, but the silicon structure to be oxidized must be maintained remote from and protected from the UV source, either within or exterior to the oxidation furnace. Atomic nitrogen can be remotely generated for thermal reaction together with atomic oxygen to form nitrogen-doped silicon dioxide.
A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description and the accompanying drawings which set forth illustrative embodiments in which the principles of the invention are utilized.